Anyone using a Whoot band (terrible name).
I don't love the subscription model, and I'm not training enough right now to be getting fatigued enough for it to really matter, but it seems like a really interesting idea. I'm sure someone else (Garmin) will have one soon to compete. Looks like nobody else has quite the same thing including the HRV, resting heart rate, sleep tracking all in one.
I've also heard that sleep tracking stuff is causing some people to get less sleep because they get anxious about getting good sleep so they can't sleep, lol.